The Fermi Gamma-Ray Space Telescope now has a full year’s worth of data, having collected some 10 million photons with measured energies from 30 MeV up to 1 TeV, with nearly uniform coverage over the entire sky. This represents an enormous increase in precision and sensitivity over previous data sets. I will review what we have already learned and hope to learn, in terms of understanding the origins of these gamma rays, including pulsars (spinning neutron stars), supermassive black holes responsible for active galactic nuclei and gamma ray bursts. We expect to measure the effect of attenuation due to extra galactic background light. The most copious distant source of gamma rays is due to interactions of cosmic rays with the material in the galaxy itself, not intrinsically interesting, but vital to understand as it is a background for all the other processes, especially including the search for dark matter, and possible extra galactic diffuse emission.

Using Investigative Science Learning Environment (ISLE) to help students learn physics and think like scientists

In this colloquium I will describe the goals, the structure, and the instructional approaches of the Investigative Science Learning Environment (ISLE) – a comprehensive introductory physics learning system that engages students in the processes that mirror scientific practices when they learn physics. The main focus of ISLE is on helping students understand “how they know what they know”, use the language of science to acquire and communicate this understanding, and practice being a scientists when facing new problems. Although a variety of curriculum materials support the learning system (the Physics Active Learning Guide, the website with more than 200 videotaped experiments with supporting questions, a complete lab curriculum with self assessment built in), ISLE is more of a philosophy of active learning and teaching than the structured curriculum. I will discuss the important aspects of this philosophy and practical ways to use it in a classroom.

I sketch a theory of what meaning and understanding are and a project based on this theory to create a program that understands.

I define understanding a domain to mean that you are able to retrieve or rapidly generate computer code that analyzes and solves most new problems as they arise in it. This contrasts with the abilities of most programs we write, which are crafted to deal with problems already seen. Understanding requires a powerful library of modules that have meaning in the sense that they exploit underlying structure of the domain, and methods to rapidly compose them into new solutions.

Evolution discovered meaningful modules. In fact, that’s why its so effective. As evolution discovers meaning, a high fraction of random mutations become meaningful— have functional consequences, such as reshaping biological systems in functional ways. So evolution essentially understands.

Human thought builds on the discoveries of evolution. We build arrangements of meaningful modules looking for the right one to solve a new problem. Because we search only over meaningful possibilities, the search is short and we can rapidly produce code to solve many new problems that arise in the world.

Attempts at designing Artificial General Intelligence (AGI) have not come to grips with the nature of understanding. People do not have introspective access to the internals of the meaningful modules: we perceive only at the meaning level and have no access to the levels that support it. Designing the underlying modules is too hard a task for unaided humans. Automatically creating the whole understanding program would require competing with Evolution, which had vastly greater computational resources than we will ever have.

I propose Artificial Genie, a system that will provide an environment where humans collaborate with automatic systems on the development of robust computer programs. Using this I propose to build a program that understands interesting domains. Novel aspects of Artificial Genie support mental imagery in a way that makes concrete how modules and agents exploit underlying structure of the physical and mathematical world and that naturally supports communication between agents; a planning system that utilizes the mental image to follow only causally relevant possibilities, reproducing introspection in cases considered to date; scaffolds that greatly speed construction of new, meaningful programs and that capture insights from evolution; economic frameworks able to motivate efficient assembly of programs and scaffolds; and natural incorporation of each of these things in module creation and program assembly.

I will describe recent experimental results, where we realize an asymmetric optical potential barrier for ultracold Rb 87 atoms using laser light tuned near the D2 optical transition. Such a one-way barrier, where atoms impinging on one side are transmitted but reflected from the other, is a realization of Maxwell’s demon and has potential implications for cooling atoms and molecules not amenable to standard laser-cooling techniques. In our experiment, atoms are confined to a far-detuned dipole trap consisting of a single focused Gaussian beam, which is divided near the focus by the barrier. The one-way barrier consists of two focused laser beams oriented almost normal to the dipole-trap axis. The first beam is tuned to present a state-dependent potential to the atoms. The second beam pumps the atoms irreversibly to the proper state on the reflecting side of the barrier, thus producing the asymmetry. We study experimentally the reflection and transmission dynamics of ultracold atoms in the presence of the one-way barrier. I will also describe our longer-term interests and efforts towards quantum measurement and control of the center-of-mass motion of atoms, including some preliminary theoretical results on atomic dynamics under inhomogeneous position measurements.

Special event at 7:30 pm at Beall Concert Hall.

This talk will give an overview of recent exciting developments in the field of metallic helical magnets (prototype: MnSi). These include: Spin-liquid phases, non-Fermi-liquid behavior, suppressed and restored quantum phase transitions, and a possible topological (“skyrmion”) ground state in parts of the phase diagram. Analogies between helimagnets (“hard” condensed matter) and liquid crystals (“soft” condensed matter) will be stressed. A puzzle and its proposed resolution that results from competing energy scales in the presence of an external magnetic field will also be discussed.

When Dave Soper invited me to present a Physics Department Colloquium, he mentioned that the new faculty and students in the Physics Department are unlikely to know about the history of zebrafish at the University of Oregon, and why this species has become a research priority for the National Institutes of Health and around the world. In this talk I will first present an historical perspective focusing on the contributions of George Streisinger that propelled zebrafish into the limelight and moved research on zebrafish genetics and development from a Eugene cottage industry to a worldwide enterprise. I will then illustrate applications of the zebrafish model by discussing one project in my laboratory in which we are using zebrafish to understand how motoneurons develop and innervate appropriate muscles. I will attempt to demonstrate some of the kinds of questions that can be addressed using zebrafish, including some of the technical limitations. I will end by putting this work into the larger context of what we can learn by studying an animal model.

The Linac Coherent Light Source (LCLS) at SLAC National Laboratory has begun operation as the world’s brightest light source and first hard x-ray free electron laser. In this talk I will review how it can be used to study materials properties on ultrasmall lengthscales and ultrashort timescales, and how it offers unique possibilities of collaboration between theory and experiment across many scientific disciplines. Specifically, I will discuss numerical simulations and experiments for photon-based spectroscopies that reveal the private dancing of electrons, spins, and atoms in strongly correlated materials.